CS pathways in practice

Question 1

Olfactory epithelium

Answer 1

~ contains sensory neurons with 12 sensory cilia each
~ sensory neurones converge into the olfactory bulb
~ contain 1x10^6 sensory neruons

Question 2

Odorant receptors

Answer 2

~ members of the 7TM-receptor family
~ highly conserved
~ >1000 olfactory receptors

Question 3

Odorant receptor mechanism (4)

Answer 3

~ odorant binds to GPCR
~ G-protien activates adenylate cyclase –> produces cAMP
~ cAMP opens a cAMP-gated ion channel = allows Na+ and Ca2+ into the cell
~ activation of voltage-gated Na+ channel in cell body triggers action potential

Question 4

What is the range of visible light?

Answer 4

300nm to 750nm

Question 5

Human rod cells

Answer 5

~ contain 1000 rhodopsin-containing discs

~ connected to bipolar neurons –> ganglion neurons –> the optic nerve

Question 6

Rhodopsin mechanism

Answer 6

~ light activates rhodopsin = trans-form
~ activates Ga’ complex
~ activates phosphodiesterase which hydrolyses cGMP –> GMP
~ the lack of cGMP closes Na+ channels –> indicating light

Question 7

Rhodopsin mechanism

Answer 7

~ light activates rhodopsin = trans-form
~ activates Ga’ complex
~ activates phosphodiesterase which hydrolyses cGMP –> GMP
~ the lack of cGMP closes cGMP-gated ion channels in PM (Na+ and Ca2+) –> indicating light
~ channel closure causes PM hyperpolarisation
~ PM hyperpolarisation reduces the release of the neurotransmitter glutamate release

Question 8

Rhodopsin mechanism (6)

Answer 8

1. light activates rhodopsin = cis form –> trans-form
2. activates Ga’ complex
3. activates phosphodiesterase which hydrolyses cGMP –> GMP
4. the lack of cGMP closes cGMP-gated ion channels in PM (Na+ and Ca2+) –> indicating light
5. channel closure causes PM hyperpolarisation
6. PM hyperpolarisation reduces the release of the neurotransmitter glutamate release

Question 9

Open to closed guard cell is caused by…

Answer 9

~ decreased turgor
~ loss of K+
~ loss of Cl-
~ loss of malate2-

Question 10

Closed to open guard cell is caused by…

Answer 10

~ increased turgor
~ gain of K+
~ gain of Cl-
~ gain of malate2-

Question 11

Which molecules are used for signalling in guard cells?

Answer 11

~ Ca2+

~ ABA (abscisic acid) - produced in response to drought + closes guard cells

Question 12

Calcium-ABA signalling in guard cells (7)

Answer 12

1. ABA causes in increase (amplification) in intracellular Ca2+ lvls - either from vacuole (SV) or outside cell
2. Ca2+ inhibits K+(in) channels
3. Ca2+ inhibits H+ (ATPase)
4. Ca2+ activates anion channels (out)
5. Ca2+ activates VK = vacuole K+(in) channel
   - causes depolarisation of PM as increased +ve ions
6. depolarisation of PM activates K+(out) channels
7. cytosolic alkalisation (increase pH) enhances K+(out)

Question 13

Ca2+-induced Ca2+ release

Answer 13

1. influx of Ca2+ through PM Ca2+ permeable channels
2. increase in [Ca2+]cyt
3. activation of SV(slow vacuolar) Ca2+ channels
   = 2nd messenger-induced increases in [Ca2+]